Remedies to prevent cracking in a liquid system

ABSTRACT

A liquid cooling system utilizing minimal size and volume enclosures, air pockets, compressible objects, and flexible objects is provided to protect against expansion of water-based solutions when frozen. In such a system, pipes, pumps, and heat exchangers are designed to prevent cracking of their enclosures and chambers. Also described are methods of preventing cracking in a liquid cooling system. In all these cases, the system must be designed to tolerate expansion when water is frozen.

RELATED APPLICATION

[0001] This application claims priority under 35 U.S.C. § 119(e) of theco-pending U.S. provisional patent application Serial No. 60/444,269,filed on Jan. 31, 2003, and titled “REMEDIES FOR FREEZING IN CLOSED-LOOPLIQUID COOLING FOR ELECTRONIC DEVICES.” The provisional patentapplication Serial No. 60/444,269, filed on Jan. 31, 2003, and titled“REMEDIES FOR FREEZING IN CLOSED-LOOP LIQUID COOLING FOR ELECTRONICDEVICES” is hereby incorporated by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to an apparatus and method ofpreventing cracking of a liquid system, such as may be useful fortransferring heat from electronic devices and components thereof. Inparticular, the invention utilizes a variety of means and objects toprotect against expansion of water-based solutions when frozen.

BACKGROUND OF THE INVENTION

[0003] When water or many other fluid mixtures are cooled belowfreezing, the material changes from a liquid state to a solid state, andundergoes a significant expansion in volume, which is as much as 10% ormore for water or water-based mixtures. When water freezes in a pipe, itundergoes a similar expansion. Water that has frozen in pipes or otherconfined spaces does more than simply clog the pipes and block flow.When freezing occurs in a confined space like a steel pipe, the ice willexpand and exert extreme pressure which is often enough to crack thepipe and cause serious damage. This phenomenon is a common failure modein hot-water heating systems and automotive cooling systems.

[0004] Ice forming in a pipe does not always cause cracking where iceblockage occurs. Rather, following a complete ice blockage in a pipe,continued freezing and expansion inside the pipe can cause waterpressure to increase downstream. The increase in water pressure leads topipe failure and/or cracking. Upstream from the ice blockage the watercan retreat back towards its inlet source, and there is little pressurebuildup to cause cracking.

[0005] Liquid cooling systems for electronic devices are occasionallysubjected to sub-freezing environments during shipping, storage, or inuse. Since these systems are going to be frozen on occasion, they mustbe designed to tolerate the expansion of water when frozen. Additives,such as antifreeze, are potentially poisonous and flammable and candamage mechanical components, sensitive sensors, and electronics, whichis why pure or substantially pure water is typically the coolant ofchoice.

[0006] What is needed is an apparatus for and method of preventingcracking in a liquid cooling system that can tolerate a predeterminedlevel of freezing and expansion inside confined spaces without damagingelectronic components or affecting system performance.

SUMMARY OF THE INVENTION

[0007] A liquid system utilizing size and volume reducing means, airpockets, compressible objects, and flexible objects is provided toprotect against expansion of water-based solutions when frozen. In sucha system, pipes, pumps, and heat exchangers are designed to preventcracking of their enclosures and chambers.

[0008] In a first aspect of the invention, an apparatus for preventingcracking of a liquid system is disclosed. The apparatus comprises atleast one heat exchanger; one or more inlet ports extending through afirst opening for conveying a fluid to a plurality of channels andpassages; one or more outlet ports extending through a second openingfor discharging the fluid from the plurality of channels and passages;and one or more compressible objects positioned substantially adjacentthe inlet ports and the outlet ports in an unpressured condition suchthat the compressible objects reduce a volume of the inlet ports and theoutlet ports and further wherein pressure exerted on the compressibleobjects increases a volume of the inlet ports and the outlet ports.

[0009] The compressible objects can preferably accommodate apredetermined level of fluid expansion. The predetermined level of fluidexpansion can be between 5 to 25 percent. The compressible objects arepreferably capable of contracting and expanding between a minimum volumeand a maximum volume. The compressible objects can be secured within theinlet port and the outlet port. Alternatively, the compressible objectscan be positioned at any location throughout the system. Thecompressible objects can be made of sponge, foam, air-filled bubbles,balloons and encapsulated in a hermetically sealed package. The packagecan be made of metallic material, metallized plastic sheet material, orplastic material. The plastic materials can be selected from teflon,mylar, nylon, PET, PVC, PEN or any other suitable package.

[0010] In a second aspect of the invention, an apparatus for preventingcracking of a liquid system is disclosed. The apparatus comprises atleast one heat exchanger having a top element and a bottom element; aplurality of channels and passages formed within the bottom element toprovide flow of a fluid therethrough; and one or more compressibleobjects positioned within one or more of the plurality of channels andpassages such that in an uncompressed state the compressible objectsreduce a volume of each of the plurality of channels and passages havingone or more of the compressible objects and further wherein underpressure exerted within the channels and passages the compressibleobjects are compressed to increase the volume of each of the pluralityof channels and passages.

[0011] In a further separate aspect of the invention, an apparatus forpreventing cracking of a liquid system is provided. The systempreferably includes one or more pumps and one or more heat exchangers.The apparatus comprises an enclosure, wherein a size and volume occupiedby fluid within the enclosure is minimized. The pump can be anelectro-osmotic pump.

[0012] The enclosure is preferably capable of contracting and expandingbetween a minimum size and volume condition and a maximum size andvolume condition.

[0013] In a second separate aspect of the invention, an apparatus forpreventing cracking of a liquid system is disclosed. The apparatuscomprises a housing having at least one inlet chamber and at least oneoutlet chamber, wherein a size and volume occupied by fluid within theinlet and outlet chambers is minimized.

[0014] The inlet and outlet chambers are preferably capable ofcontracting and expanding between a minimum size and volume conditionand a maximum size and volume condition. The inlet and outlet chamberscan be separated by a pumping structure or mechanism.

[0015] In a further separate aspect of the invention, a method ofpreventing cracking of a liquid system is disclosed. The system includesat least one pump and at least one heat exchanger. The method comprisesthe steps of providing an enclosure and minimizing a size and volumeoccupied by fluid within the enclosure.

[0016] In a further aspect of the invention, a method of preventingcracking of a liquid system is disclosed. The method comprises the stepsof providing a housing having at least one inlet chamber and at leastone outlet chamber; and minimizing a size and volume occupied by fluidwithin the inlet and outlet chambers.

[0017] In a further aspect of invention, an apparatus for preventingcracking of a liquid system is provided. The system includes at leastone pump and at least one heat exchanger. The apparatus comprises anenclosure and one or more compressible objects immersed in theenclosure.

[0018] The objects preferably accommodate a predetermined level of fluidexpansion. The predetermined level of fluid expansion is preferablybetween 5 to 25 percent. The objects preferably have a size and volumeproportion to an amount of fluid in the enclosure. The objects can be ahydrophobic foam. Alternatively, the objects can be hydrophobic sponges.Also, the objects can be balloons in hydrophobic bags. The objects canbe made of rubber, plastic, foam, sealed foam or rubber, or vacuumlaminated foam or rubber. The objects may be enclosed in vacuumlaminated bags.

[0019] In a further aspect of the invention, an apparatus for preventingcracking of a liquid system is provided. The apparatus comprises ahousing having at least one inlet chamber and at least one outletchamber and one or more compressible objects immersed in the inlet andoutlet chambers. The objects preferably have a size and volumeproportional to an amount of fluid in the chambers.

[0020] In a further aspect of the invention, a method of preventingcracking of a liquid system is disclosed. The method comprises the stepsof providing an enclosure and immersing one or more compressible objectsin the enclosure.

[0021] In a further aspect of the invention, a method of preventingcracking of a liquid system is disclosed. The method comprises the stepsof providing a housing having at least one inlet chamber and at leastone outlet chamber and immersing one or more compressible objects in theinlet and outlet chambers.

[0022] In a further aspect of the invention, an apparatus for preventingcracking of a liquid system is disclosed. The apparatus comprises anenclosure and one or more air pockets disposed in the enclosure. The airpockets are preferably positioned farthest away from a location whereliquid begins to freeze in the enclosure.

[0023] The air pockets preferably have a volume proportional to anamount of fluid in the enclosure. The air pockets preferably accommodatea predetermined level of fluid expansion. The predetermined level offluid expansion is preferably between 5 to 25 percent.

[0024] In a further aspect of the invention, an apparatus for preventingcracking of a liquid system is disclosed. The apparatus comprises ahousing having at least one inlet chamber and at least one outletchamber and an one or more air pockets disposed in the inlet and outletchambers. The air pockets are preferably positioned farthest away from alocation where liquid begins to freeze in the chambers. The air pocketspreferably have a volume proportion to an amount of fluid in thechambers.

[0025] In a further aspect of the invention, a method of preventingcracking of a liquid system is provided. The method comprises the stepsof providing an enclosure and disposing one or more air pockets in theenclosure. The air pockets are positioned farthest away from a locationwhere liquid begins to freeze in the enclosure.

[0026] In a further aspect of the invention, a method of preventingcracking of a liquid system is disclosed. The method comprises the stepsof providing a housing having at least one inlet chamber and at leastone outlet chamber and disposing one or more air pockets in the inletand outlet chambers. The air pockets are positioned farthest away from alocation where liquid begins to freeze in the chambers.

[0027] In a further aspect of the invention, an apparatus for preventingcracking of a liquid system is provided. The apparatus comprises anenclosure for holding liquid having a plurality of walls and at leastone flexible object coupled to form a portion of at least one wall ofthe enclosure such that pressure exerted on the flexible objectsincreases a volume of the enclosure.

[0028] The flexible objects preferably accommodate a predetermined levelof fluid expansion. The flexible objects can be spaced apart apredetermined distance. The flexible objects are preferably capable ofcontracting and expanding between a minimum volume condition and amaximum volume condition. The flexible objects are preferably securedwithin the enclosure and deformable under pressure. The flexible objectscan be made of rubber. Alternatively, the flexible objects can be madeof plastic or foam.

[0029] In a further aspect of the invention, an apparatus for preventingcracking of a liquid system is provided. The apparatus comprises ahousing having at least one inlet chamber and at least one outletchamber and at least one flexible object coupled to form a portion of atleast one of the inlet and outlet chambers such that pressure exerted onthe flexible objects increases a volume of the housing. The flexibleobjects preferably accommodate a predetermined level of fluid expansion.

[0030] In a further aspect of the invention, a method of preventingcracking of a liquid system is disclosed. The method comprises the stepsof providing an enclosure and disposing at least one flexible object toform a portion of at least one wall of the enclosure such that pressureexerted on the flexible objects increases a volume of the enclosure. Theflexible objects preferably accommodate a predetermined level of fluidexpansion.

[0031] In a further aspect of the invention, a method of preventingcracking of a liquid system is disclosed. The method comprises the stepsof providing a housing having at least one inlet chamber and at leastone outlet chamber and disposing at least one flexible object to form aportion of at least one of the inlet and outlet chambers such thatpressure exerted on the flexible objects increases a volume of thehousing. The flexible objects preferably accommodate a predeterminedlevel of fluid expansion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032]FIG. 1 illustrates a schematic diagram of a conventionalclosed-loop cooling system, which includes an electro-osmotic pump and aheat exchanger.

[0033]FIG. 2 illustrates a schematic diagram of a housing having aninlet chamber and an outlet chamber.

[0034]FIG. 3 illustrates a schematic diagram of a housing having inletand outlet chambers reduced in size and volume in accordance with thepresent invention.

[0035]FIG. 4 illustrates a schematic diagram of an air pocket disposedin an inlet chamber and an outlet chamber of a housing in accordancewith the present invention.

[0036]FIG. 5 illustrates a schematic diagram of a compressible objectdisposed in an inlet chamber and an outlet chamber of a housing inaccordance with the present invention.

[0037]FIG. 6A illustrates a schematic diagram of a housing having inletand outlet chambers and a plurality of spaced apart flexible objectscoupled to the chambers.

[0038]FIG. 6B illustrates a schematic diagram of a housing having inletand outlet chambers and a plurality of spaced flexible objects coupledto the chambers, the flexible objects being displaced during fluidexpansion to prevent cracking.

[0039]FIG. 7A illustrates a schematic diagram of compressible objectscoupled to inlet and outlet ports within a heat exchanger.

[0040]FIG. 7B illustrates a schematic diagram of compressible objectsdisposed along a bottom surface of a heat exchanger within adjacentmicrochannels.

[0041]FIG. 8A illustrates a schematic diagram of compressible objectscoupled to walls of fluid filled tubing within a heat rejector.

[0042]FIG. 8B illustrates a schematic diagram of compressible objectsdisposed along a length of fluid filled tubing within a heat rejector.

[0043]FIG. 9 illustrates a schematic diagram of compressible objectsdisposed within fluid filled channels of a plate within a heat rejector.

[0044]FIG. 10 illustrates a schematic diagram of compressible objectsdisposed in fluid segments of a cooling loop.

[0045]FIG. 11 illustrates a schematic diagram of a housing having aninlet chamber and an outlet chamber and a plurality of spaced apartflexible objects coupled to the chambers.

[0046]FIG. 12 illustrates a schematic diagram of a housing having inletand outlet chambers and a plurality of spaced apart flexible objectscoupled to the chambers, the flexible objects being displaced duringfluid expansion to prevent cracking.

[0047]FIG. 13 illustrates a flow chart illustrating steps of a preferredmethod of one embodiment of the present invention.

[0048]FIG. 14 illustrates a schematic diagram of a housing having inletand outlet chambers having a relatively narrowed central portion andsubstantially identical expanded end portions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0049] Reference will now be made in detail to the preferred andalternative embodiments of the invention, examples of which areillustrated in the accompanying drawings. While the invention will bedescribed in conjunction with the preferred embodiments, it will beunderstood that they are not intended to limit the invention to theseembodiments. On the contrary, the invention is intended to coveralternatives, modifications and equivalents, which may be includedwithin the spirit and scope of the invention as defined by the appendedclaims. Furthermore, in the following detailed description of thepresent invention, numerous specific details are set forth in order toprovide a thorough understanding of the present invention. However, itshould, be noted that the present invention may be practiced withoutthese specific details. In other instances, well known methods,procedures and components have not been described in detail as not tounnecessarily obscure aspects of the present invention.

[0050]FIG. 1 shows a schematic diagram of a closed-loop cooling system100, which includes heat exchanger 20 attached to a heat producingdevice 55 (shown as an integrated circuit attached to a circuit board,but which could also be a circuit board or other heat producing device),a pump 30 for circulating fluid, a heat rejector 40, which may include aplurality of fins 46 for further assisting in conducting heat away fromthe system 100, and a controller 50 for a pump input voltage based on atemperature measured at the heat exchanger 20. Fluid flows from an inlet32, is pulled through a porous structure (not shown) within the pump 30by electroosmotic forces, and exits through the outlet 34. While thepreferred embodiment uses an electroosmotic pump, it will be understoodthat the present invention can be implemented in a system using othertypes of pumps.

[0051] Still referring to FIG. 1, the fluid travels through the heatexchanger 20 and the heat rejector 40 through tubing lengths 114 and 110before being recycled back to the inlet 32 of the pump 30 via anothertubing 112. The controller 50 is understood to be an electronic circuitthat takes input signals from thermometers in the heat exchanger 20, orfrom thermometers in the device 55 being cooled, which signals aretransmitted along signal lines 120. The controller 50, based upon theinput signals regulates flow through the pump 30 by applying signals toa power supply (not shown) associated with the pump 30 along signallines 122 to achieve the desired thermal performance.

[0052] As fluid temperature drops below freezing, ice forms into ablockage. Continued growth of ice in areas of the system 100 can lead toexcessive fluid pressure. The resulting pressure can rupture or damageindividual elements, such as the lengths 110, 112, 114 of tubing,channels in the heat exchangers 20 and 40, and/or chambers inside thepump 30. As will be explained and understood in further detail below,the individual elements must be designed in a way that toleratesexpansion of the fluid or water when frozen.

[0053] In one embodiment, shown in FIG. 2, an apparatus or pump 60includes a housing 68 having an inlet chamber 62 and an outlet chamber64. A pumping mechanism or structure 69 separates the inlet and outletchambers 62 and 64 from a bottom surface of the housing 68 to an uppersurface of the housing 68. The pumping structure 69 channels liquid froma pump inlet 61 to a pump outlet 66. The chambers 62 and 64 are filledwith fluid. Preferably, the liquid used in the pump 60 is water. It iscontemplated that any other suitable liquid is contemplated inaccordance with the present invention.

[0054] Still referring to FIG. 2, the pump 60 can be designed so thatthere are no large pockets of water in any of the chambers 62 and 64.Since water expands as it freezes, ice takes up more room than liquid.When freezing occurs in confined spaces, such as chambers 62 and 64,displacement caused by the expansion of fluids is proportional to anamount of fluid volume in the chambers 62 and 64. Minimizing the sizeand volume occupied by the chambers 62 and 64 reduces the displacement,and thereby prevents bending, stretching, or cracking of the chambers 62and 64.

[0055] As shown in FIG. 3, the volume of inlet and outlet chambers 72and 74 is substantially reduced compared to the chambers 62 and 64 inFIG. 2. As such, the amount of water present in the pump 70 is greatlyreduced. Detailed mechanical analysis of the chambers 72 and 74 isrequired, but the chambers 72 and 74 can be designed to withstand forceexerted by frozen water. The inlet and outlet chambers 72 and 74 can becapable of contracting and expanding between a minimum size and volumecondition and a maximum size and volume condition. It should beunderstood that the tubing lengths 110, 112, and 114 in FIG. 1 can bereduced in size and volume to reduce displacement caused by fluidexpansion in areas of the system 100 (FIG. 1).

[0056] In another embodiment, as shown in FIG. 4, an apparatus or pump80 includes a housing 88 having an inlet chamber 82 and an outletchamber 84. A pumping structure 89 separates the inlet and outletchambers 82 and 84 from a bottom surface of the housing 88 to an uppersurface of the housing 88. The pumping structure 89 channels liquid froma pump inlet 81 to a pump outlet 86. The chambers 82 and 84 are filledwith fluid to a large extent. Preferably, the liquid used in the pump 80is water. It is contemplated that any other suitable liquid iscontemplated in accordance with the present invention.

[0057] Still referring to FIG. 4, air pockets 85 and 87 are disposed inthe inlet and outlet chambers 82 and 84. The air pockets 85 and 87 arepreferably positioned farthest away from a location where fluid beginsto freeze in the chambers 82 and 84. Expansion of the ice upon freezingin the chambers 82 and 84 will take up some space occuppied by the airpockets 85 and 87, and a cause a slight increase of pressure in thechambers 82 and 84. However, air is compressible enough that it can besignificantly compressed with relatively small forces, such that theexpansion of the ice is easily accommodated. Preferably, the air pockets85 and 87 have a volume proportion to an amount of fluid in the chambers82 and 84. The air pockets 85 and 87 can preferably accommodate apredetermined level of fluid expansion between five to twenty fivepercent.

[0058] As mentioned before, ice forming in a confined space does nottypically cause a break where initial ice blockage occurs. Rather,following a complete ice blockage in a confined space, continuedfreezing and expansion inside the confined space cause fluid pressure toincrease downstream. The fluid pressure will reach a maximum at a lastlocation to freeze in a hermetically sealed system. The pressure can bevery large, unless there is a trapped air pocket in that region. Thermaldesign of the chambers 82 and 84 can be altered to select a locationwhere the fluid begins to freeze, and to arrange for freezing to startfrom one location and advance continuously towards an air pocket atanother location. For example, if there is an air pocket at the topsurface of a chamber, the fluid should be nucleated at the bottomsurface of the chamber. As the fluid begins to freeze at the bottomsurface of the chamber, ice expansion displaces water and compresses theair pocket. Since air is easily compressible, the chamber can freezecompletely without generating large forces at any location in thechamber.

[0059] To arrange a location of initial freezing in the chamber, it maybe necessary to provide a thermal path from the location of initialfreezing to its surroundings. As the fluid or chamber is cooled fromabove a freezing point, the thermal path serves to efficiently rejectheat stored in the location. For example, an optional metallic insert288 is mounted from the location of initial freezing in the chamber tothe top surface of the chamber would serve. Preferably, the metallicinsert 288 is formed of a material that will not contaminate the fluidsuch as copper. Alternatively, reducing the size and volume of thechamber or reducing package insulation in the chamber could also work. Acritical factor is use of any material or structure that assists aparticular location become cold fastest, and so that progression offreezing is continuous from that location to the air pockets 85 and 87of FIG. 4.

[0060] In some cases, it may be difficult to control the positioning andlocation of the air pockets 85 and 87 in the chambers 82 and 84.Further, it may be difficult to dispose an air pocket in each chamber ofthe system 100 (FIG. 1). In a further embodiment, as shown in FIG. 5,one or more compressible objectss 95 and 97 are immersed in pump 90. Thepump 90 includes a housing 98 having an inlet chamber 92 and an outletchamber 94. A pumping structure 99 separates the inlet and outletchambers 92 and 94 from a bottom surface of the housing 98 to an uppersurface of the housing 98. The pumping structure 99 channels liquid froma pump inlet 91 to a pump outlet 96. The chambers 92 and 94 are filledwith fluid to a large extent. Preferably, the liquid used in the pump 90is water. It is contemplated that any other suitable liquid iscontemplated in accordance with the present invention.

[0061] Still referring to FIG. 5, the one or more compressible objectss95 and 97 are immersed and coupled to inlet and outlet chambers 92 and94. The objects 95 and 97 can be a hydrophobic foam or sponge.Preferably, the objects 95 and 97 accommodate a predetermined level offluid expansion between five to twenty five percent. To accommodate thefluid expansion, the objects 95 and 97 can preferably have a size andvolume proportional to an amount of fluid in the chambers 92 and 94.

[0062] The objects 95 and 97 can be comprised of a compressiblematerial, such as an open-cell or closed-cell foam, rubber, sponge,air-filled bubbles, elastomer, or any related material, and a protectivelayer covering all surfaces of the compressible material. A purpose ofhaving the protective layer is to prevent contact between thecompressible material and a surrounding fluid. The protective layer canbe formed by many means, including wrapping and sealing, dip-coating,spray-coating, or other similar means. The protective layer can be avacuum laminated cover, such as a spray-on layer, a deposited layer, ora layer formed by reacting or heating surfaces of the compressiblematerial. In addition, it is possible to form a protective layer on thesurface of the compressible material by thermally fusing, melting, orchemically modifying the surface. The protective layer can be flexibleenough so that a volume of the compressible material can be reduced bypressure. In order to achieve this degree of flexibility, the protectivelayer can be much thinner than the compressible material. Further, theprotective layer can be formed from a material that is not chemicallyattacked by the fluid used in the cooling system, or degraded bytemperature cycles above and below freezing. The protective layer can behermetically sealed so that gas cannot enter or leave the volume withinthe protective layer. The protective layer can be formed from a varietyof materials, including teflon, mylar, polyethylene, nylon, PET, PVC,PEN or any other suitable plastic, and can additionally include metalfilms on interior or exterior surfaces to improve hermeticity. Inaddition, the protective layer can be a metallized plastic sheetmaterial, as used in potato chip packaging, and can serve as animpervious layer, blocking all gas and liquid diffusion. Furthermore, incases where occasional bubbles are moving through the cooling system, aswhen an electroosmotic pump is generating hydrogen and oxygen gasbubbles, the protective layer can be hydrophilic to help reduce thepossibility that the bubbles will attach to the surfaces.

[0063] In a further embodiment, as shown in FIG. 6A, an apparatus orpump 103 includes a housing 108 having an inlet chamber 102 and anoutlet chamber 104. A pumping structure 109 separates the inlet andoutlet chambers 102 and 104 from a bottom surface of the housing 108 toan upper surface of the housing 108. The pumping structure 109 channelsliquid from a pump inlet 101 to a pump outlet 106. The chambers 102 and104 are filled with fluid to a large extent. Preferably, the liquid usedin the pump 103 is water. It is contemplated that any other suitableliquid is contemplated in accordance with the present invention.

[0064] Still referring to FIG. 6A, a plurality of spaced apart flexibleobjects 105 and 107 are coupled to the inlet and outlet chambers 102 and104. In this embodiment, the flexible objects 105 and 107 are preferablyconstructed from a flexible material, such as rubber or plastic. Theflexible material is preferably designed and arranged such that it canbe partially displaced to accommodate expansion of ice without crackingitself or other rigid elements of the inlet and outlet chambers 102 and104. Preferably, the flexible objects 105 and 107 accommodate apredetermined level of fluid expansion between five to twenty fivepercent. The flexible objects can be spaced apart from one another apredetermined distance. Preferably, the flexible objects 105 and 107 arecapable of contracting and expanding between a minimum volume conditionand a maximum volume condition. Alternatively, the flexible objects 105and 107 are secured within the chambers 102 and 104.

[0065]FIG. 7A illustrates a schematic diagram of compressible objects132 and 134 coupled to inlet and outlet ports 131 and 135 within a heatexchanger 130. Fluid generally flows from one or more inlet ports 131and flows along a bottom surface 137 in microchannels 138 of anyconfiguration and exits through the outlet port 135, as shown by arrows.The compressible objects 132 and 134 are preferably designed andarranged such that it can be partially displaced to accommodateexpansion of ice without cracking itself or other rigid elements of theinlet and outlet ports 131 and 135 in FIG. 7A.

[0066]FIG. 7B illustrates a schematic diagram of compressible objects145 disposed along a bottom surface 147 of a heat exchanger 140 withinmicrochannels 148. As shown in FIG. 7B, the compressible objects 145 canbe arranged within the microchannels 148 such that the compressibleobjects 145 form part of a seal from a top surface 149 to the bottomsurface 147. In both FIGS. 7A and 7B, compressible objects act as freezeprotection within a heat exchanger. The positioning of the compressibleobjects 145 is intended to minimize flow resistance, and to avoiddegrading heat transfer from the bottom surface 147 to the fluid.Placement of the compressible objects 145 on sides of the microchannelsis also possible, although less advantageous than the positioning asshown in FIG. 8A. Positioning on the bottom surface 148 would severelydegrade performance of the heat exchanger 140 because of a high thermalresistance of the compressible objects 145.

[0067]FIG. 8A illustrates a schematic diagram of compressible objects152 and 154 coupled to walls 151 and 155 of fluid filled tubing 150within a heat rejector. The tubing 150 can be substantially longer thanother portions of the system, for example centimeters in length incertain parts of the system 100 (FIG. 1), and as much as a meters inlength in other parts. Placement of a length of the compressible objects152 and 154 to the walls 151 and 155 of the tubing 150 will act asfreeze protection within a heat rejector. Alternatively, as shown inFIG. 8B, compressible element 165, such as compressible foam structures,can be threaded along a length of the tubing 160. The compressibleelement 165 can float freely within the tubing 160. Because thecompressible element 165 is thinner than the tubing 160, it can simplybe threaded without concern for forming a blockage in the tubing 160. Alength of the compressible elements 165 will vary according to thelengths of the tubing 160.

[0068]FIG. 9 illustrates a schematic diagram of various possibleconfigurations for compressible objects 171, 173, 175 and 177 disposedwithin fluid filled channels 170 of a plate 180 within a heat rejector.As shown in FIG. 9, fluid can be routed through the channels 170disposed within the plate 180 that allows fluid flow between a fluidinlet 172 and a fluid outlet 174. A heat rejector can include fins 190mounted to and in thermal contact with the plate 180. The compressibleobjects 171, 173, 175 and 177 disposed within the channels 170 providefreeze protection, thereby improving performance of the entire system.

[0069] In addition to the use of size and volume reducing means, airpockets, compressible objects, and compressible objects discussed above,other techniques can be used to prevent cracking in a liquid coolingsystem, as would be recognized by one of ordinary skill in the art. Forexample, as shown in FIG. 10, compressible elements can partly fill allfluid segments of a cooling loop. In all these cases, it will beappreciated by one of ordinary skill that routine mechanical designanalysis is useful to compute stress throughout the cooling systemincluding but not limited to the chambers, lengths of tubing, and otherenclosures that contain either the air pockets and compressible objectsto design a system for which that stresses do not accumulate in anylocation in sizes large enough to cause the enclosures to fail. In aclosed-loop cooling system for an electronic device, relatively largereservoirs of fluid are likely to be in the chambers of the pump or thetubing in a heat exchanger. System design should strive to eliminatethese volumes of fluid, thereby reducing the reservoirs at their source.Failing that, or if large volumes of fluid are needed to guaranteesufficient fluid over extended use, the embodiments described above canreduce forces generated during freezing to manageable levels.

[0070] In another embodiment, shown in FIG. 11, an apparatus or pump 200includes a housing 208 having an inlet chamber 202 and an outlet chamber204. A pumping structure 209 separates the inlet and outlet chambers 202and 204 from a bottom surface of the housing 208 to an upper surface ofthe housing 208. The pumping structure 209 channels liquid from a pumpinlet 201 to a pump outlet 206. The chambers 202 and 204 are filled withfluid. Preferably, the liquid used in the pump 200 is water. It iscontemplated that any other suitable liquid is contemplated inaccordance with the present invention.

[0071] Still referring to FIG. 11, the housing 208 can be designed towithstand expansion of the fluid when freezing occurs. A plurality offlexible objects 210 are coupled to at least one wall of the housing208. The housing 208 consists of rigid plates and support the chambers202 and 204. The plates make up a plurality of sides of the chambers 202and 204 and are joined by the flexible objects 210. The flexible objects210 can be fastened to the plates. The flexible objects 210 can beformed on any or each of the plurality of sides of the chambers 202 and204, which includes corner edges, and allow the plates to be displacedoutward when acted upon by force, as shown in FIG. 12. The flexibleobjects can be elastomer hinges or any suitable polymer hinge, so longas it can alter its shape when met by force.

[0072] In an alternative embodiment, as shown in FIG. 13, a method ofpreventing cracking in a pump is disclosed beginning in the Step 300. Inthe Step 310, a housing is provided having an inlet chamber and anoutlet chamber separated by a pumping structure. In the Step 320, aplurality of spaced apart flexible objects are disposed form at leastone wall of the housing such that pressure exerted on the plurality ofspaced apart flexible objects increases a volume of the housing. Theflexible objects can accommodate a predetermined level of fluidexpansion.

[0073] The predetermined level of fluid can be between five to twentyfive percent. The flexible objects are preferably spaced apart apredetermined distance. Additionally, the flexible objects arepreferably capable of contracting and expanding between a minimum volumecondition and a maximum volume condition. The pump can beelectro-osmotic. The housing can include rigid plates. Furthermore, theflexible objects can be fastened to the rigid plates. The flexibleobjects can be made of rubber, plastic or foam.

[0074] In another embodiment, shown in FIG. 14, an apparatus or pump 400includes a housing 410 having hourglass-shaped inlet and outletchambers. The hourglass-shaped chambers can have a relatively narrowedmiddle or central portion 405 and substantially identical expanded endportions 407. A pumping structure 420 separates the inlet and outletchambers from a bottom surface of the housing 410 to an upper surface ofthe housing 410. The apparatus can include a thermal path from alocation of initial freezing to its surroundings.

[0075] As the fluid or chamber is cooled from above a freezing point,the thermal path serves to efficiently reject heat stored in thelocation. For example, an optional metallic insert 430 is mounted fromthe location of initial freezing in the chamber to the top surface ofthe chamber would serve. Preferably, the metallic insert 430 is formedof a material that will not contaminate the fluid such as copper. Acritical factor is use of any material or structure that assists aparticular location become cold fastest, and so that progression offreezing is continuous from that location to the expanded end portions407 of the chambers. The combination of having a hourglass-shapedchambers and the metallic insert 430 allows for freezing to initiate atthe narrowed middle or central portion 405 of the hourglass-shapedchambers and expand outward to the expanded end portions 407.

[0076] In the above-described embodiments, the present invention isapplied to a pump or a housing having an inlet chamber and an outletchamber. Alternatively, the present invention may be applied to anyenclosure in a liquid cooling system. The liquid cooling systempreferably includes an electro-osmotic pump and a heat exchanger. Assuch, the size and volume reducing means, the air pockets, thecompressible objects, and the compressible objects can be applied to anyor each enclosure in the system, including tubing, of the liquid coolingsystem.

[0077] The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modification s may be made inthe embodiment chosen for illustration without departing from the spiritand scope of the invention.

What is claimed is:
 1. An apparatus for preventing cracking of a liquidsystem, comprising: at least one heat exchanger; at least one inlet portextending through a first opening for conveying a fluid to a pluralityof channels and passages; at least one outlet port extending through asecond opening for discharging the fluid from the plurality of channelsand passages; and one or more compressible objects coupled to the inletand outlet ports in an unpressured condition such that the compressibleobjects reduce a volume of the inlet port and the outlet port andfurther wherein pressure exerted on the compressible object increases avolume of the inlet port and the outlet port.
 2. The apparatus of claim1, wherein the compressible objects accommodate a predetermined level offluid expansion.
 3. The apparatus of claim 2, wherein the predeterminedlevel of fluid expansion is between 5 to 25 percent.
 4. The apparatus ofclaim 1, wherein the compressible objects being capable of contractingand expanding between a minimum volume and a maximum volume.
 5. Theapparatus of claim 1, wherein the compressible objects being securedwithin the inlet port and the outlet port.
 6. The apparatus of claim 1,wherein the compressible objects are confined within the inlet port andthe outlet port.
 7. The apparatus of claim 1, wherein the compressibleobjects are made of one of the following: sponge, foam, air-filledbubbles, or balloons.
 8. The apparatus of claim 7, wherein the sponge orfoam is hydrophobic.
 9. The apparatus of claim 1, wherein thecompressible object is encapsulated in a gas or liquid impermeablepackage.
 10. The apparatus of claim 9, wherein the package is formed ofmetallic barrier material or metallized plastic sheet material.
 11. Theapparatus of claim 9, wherein the package has a hydrophilic surface orcoating.
 12. The apparatus of claim 9, wherein the package is formed ofplastic material.
 13. The apparatus of claim 12, wherein the plasticmaterial is selected from the group teflon, mylar, PET, PEN, PVC, orother suitable plastic materials.
 14. An apparatus for preventingcracking of a liquid system, comprising: at least one heat exchangerhaving a top element and a bottom element; a plurality of channels andpassages formed within the bottom element to provide flow of a fluidtherethrough; and one or more compressible objects positioned within oneor more of the channels and passages such that in an uncompressed statethe compressible objects reduce a volume of each of the channels andpassages having compressible objects and further wherein under pressureexerted within the channels and passages the compressible objects arecompressed to increase the volume of each of the channels and passages.15. The apparatus of claim 14, wherein the compressible objectsaccommodate a predetermined level of fluid expansion.
 16. The apparatusof claim 15, wherein the predetermined level of fluid expansion isbetween 5 to 25 percent.
 17. The apparatus of claim 14, wherein thecompressible objects being capable of contracting and expanding betweena minimum volume and a maximum volume.
 18. The apparatus of claim 14,wherein the compressible objects being positioned with a portion of thetop element.
 19. The apparatus of claim 14, wherein the compressibleobjects are made of one of the following: sponge, foam, air-filledbubbles, or balloons.
 20. The apparatus of claim 14, wherein thecompressible objects are encapsulated in a gas or liquid impermeablepackage.
 21. The apparatus of claim 20, wherein the package is formed ofmetallic barrier material or metallized plastic sheet material.
 22. Theapparatus of claim 20, wherein the package has a hydrophilic surface orcoating.
 23. The apparatus of claim 20, wherein the package is formed ofplastic material.
 24. The apparatus of claim 23, wherein the plasticmaterial is selected from the group teflon, mylar, PET, PEN, PVC, orother suitable plastic materials.
 25. An apparatus for preventingcracking of a liquid system, comprising: an enclosure; and one or morecompressible objects immersed in the enclosure.
 26. The apparatus ofclaim 25, wherein the objects accommodate a predetermined level of fluidexpansion.
 27. The apparatus of claim 26, wherein the predeterminedlevel of fluid expansion is between 5 to 25 percent.
 28. The apparatusof claim 25, wherein the objects having a size and volume proportion toan amount of fluid in the enclosure.
 29. The apparatus of claim 25,wherein the objects are a hydrophobic foam.
 30. The apparatus of claim25, wherein the object are a hydrophobic sponge.
 31. The apparatus ofclaim 25, wherein the objects are made of one of the following: sponge,foam, air-filled bubbles, or balloons.
 32. The apparatus of claim 25,wherein the objects are encapsulated in a gas or liquid impermeablepackage.
 33. The apparatus of claim 32, wherein the package is formed ofmetallic barrier material or metallized plastic sheet material.
 34. Theapparatus of claim 32, wherein the package is formed of plasticmaterial.
 35. The apparatus of claim 34, wherein the plastic material isselected from the group teflon, mylar, PET, PEN, PVC, or other suitableplastic materials.
 36. An apparatus for preventing cracking of a liquidsystem, comprising: a housing having at least one inlet chamber and atleast one outlet chamber; and one or more compressible objects immersedin the inlet and outlet chambers.
 37. The apparatus of claim 36, whereinthe objects accommodate a predetermined level of fluid expansion. 38.The apparatus of claim 37, wherein the predetermined level of fluidexpansion is between 5 to 25 percent.
 39. The apparatus of claim 36,wherein the objects having a size and volume proportion to an amount offluid in the chambers.
 40. The apparatus of claim 36, wherein theobjects are a hydrophobic foam.
 41. The apparatus of claim 36, whereinthe objects are a hydrophobic sponge.
 42. The apparatus of claim 36,wherein the objects are made of one of the following: sponge, foam,air-filled bubbles, or balloons.
 43. The apparatus of claim 36, whereinthe objects are encapsulated in a gas or liquid impermeable package. 44.The apparatus of claim 43, wherein the package is formed of metallicbarrier material or metallized plastic sheet material.
 45. The apparatusof claim 43, wherein the package is formed of plastic material.
 46. Theapparatus of claim 45, wherein the plastic material is selected from thegroup teflon, mylar, PET, PEN, PVC, or other suitable plastic materials.47. A method of preventing cracking of a liquid system, the systemincluding one or more pumps and one or more heat exchangers, the methodcomprising the steps of: providing an enclosure; and immersing one ormore compressible objects in the enclosure.
 48. The method of claim 47,wherein the objects accommodate a predetermined level of fluidexpansion.
 49. The method of claim 48, wherein the predetermined levelof fluid expansion is between 5 to 25 percent.
 50. The method of claim47, wherein the objects having a size and volume proportion to an amountof fluid in the enclosure.
 51. The method of claim 47, wherein theobjects are a hydrophobic foam.
 52. The method of claim 47, wherein theobjects are a hydrophobic sponge.
 53. The method of claim 47, whereinthe objects are made of one of the following: sponge, foam, air-filledbubbles, or balloons.
 54. The method of claim 47, wherein the objectsare encapsulated in a gas or liquid impermeable package.
 55. The methodof claim 54, wherein the package is formed of metallic barrier materialor metallized plastic sheet material.
 56. The method of claim 54,wherein the package is formed of plastic material.
 57. The method ofclaim 56, wherein the plastic material is selected from the groupteflon, mylar, PET, PEN, PVC, or other suitable plastic materials.
 58. Amethod of preventing cracking of a liquid system, the method comprisingthe steps of: providing a housing having at least one inlet chamber andat least one outlet chamber; and immersing one or more compressibleobjects in the inlet and outlet chambers
 59. The method of claim 58,wherein the objects accommodate a predetermined level of fluidexpansion.
 60. The method of claim 59, wherein the expansion occurs uponchange of phase of an enclosed material from liquid to solid.
 61. Themethod of claim 59, wherein the predetermined level of fluid expansionis between 5 to 25 percent.
 62. The method of claim 58, wherein theobjects having a size and volume proportion to an amount of fluid in thechambers.
 63. The method of claim 58, wherein the objects are ahydrophobic foam.
 64. The method of claim 58, wherein the objects are ahydrophobic sponge.
 65. The method of claim 58, wherein the objects aremade of one of the following: sponge, foam, air-filled bubbles, orballoons.
 66. The method of claim 58, wherein the objects areencapsulated in a gas or liquid impermeable package.
 67. The method ofclaim 66, wherein the package is formed of metallic barrier material ormetallized plastic sheet material.
 68. The method of claim 66, whereinthe package is formed of plastic material.
 69. The method of claim 68,wherein the plastic material is selected from the group teflon, mylar,PET, PEN, PVC, or other suitable plastic materials.
 70. An apparatus forpreventing cracking of a liquid system, the system including one or morepumps and one or more heat exchangers, comprising an enclosure, whereinthe enclosure being capable of contracting and expanding between aminimum size and volume condition and a maximum size and volumecondition.
 71. An apparatus for preventing cracking in a pump,comprising: a housing having at least one inlet chamber and at least oneoutlet chamber, the inlet and outlet chambers having a relativelynarrowed central portion and substantially identical expanded endportions; and means for initiating freezing from the narrowed centralportion to the expanded end portions.
 72. The apparatus of claim 71,wherein the means for initiating comprises at least one metallic insertmounted at a location in at least one of the inlet and outlet chambers.73. The apparatus of claim 72, wherein the metallic insert is made ofone of the following: copper, gold, silver, or a material of highthermal conductivity, such as silicon, aluminum, or a metal.
 74. Theapparatus of claim 72, wherein the metallic insert is coated with nickelor copper.
 75. A method of preventing cracking in a pump, the methodcomprising the steps of: providing a housing having at least one inletchamber and at least one outlet chamber, the inlet and outlet chambershaving a relatively narrowed central portion and substantially identicalexpanded end portions; and providing means for initiating freezing fromthe narrowed central portion to the expanded end portions.
 76. Themethod of claim 75, wherein the step of providing means for initiatingcomprises disposing at least one metallic insert at a location in atleast one of the inlet and outlet chambers.
 77. The method of claim 76,wherein the metallic insert is made of one of the following: copper,gold, silver, or a material of high thermal conductivity, such assilicon, aluminum, or a metal.
 78. The apparatus of claim 76, whereinthe metallic insert is coated with nickel or copper.
 79. An apparatusfor preventing cracking in a liquid system, comprising: an enclosure;and at least one air pocket disposed in the enclosure, the air pocketpositioned farthest away from a location where liquid begins to freezein the enclosure.
 80. The apparatus of claim 79, wherein the air pockethaving a volume proportion to an amount of fluid in the enclosure. 81.The apparatus of claim 79, wherein the air pocket accommodates apredetermined level of fluid expansion.
 82. The apparatus of claim 81,wherein the predetermined level of fluid expansion is between 5 to 25percent.
 83. An apparatus for preventing cracking of a liquid system,comprising: a housing having at least one inlet chamber and at least oneoutlet chamber; and at least one air pocket disposed in the inlet andoutlet chambers, the air pocket positioned farthest away from a locationwhere liquid begins to freeze in the chambers.
 84. The apparatus ofclaim 83, wherein the air pocket having a volume proportional to anamount of fluid in the chambers.
 85. The apparatus of claim 84, whereinthe proportional is between 5% and 25%.
 86. The apparatus of claim 83,wherein the air pocket accommodates a predetermined level of fluidexpansion.
 87. The apparatus of claim 86, wherein the predeterminedlevel of fluid expansion is between 5 to 25 percent.
 88. A method ofpreventing cracking of a liquid system, the method comprising the stepsof: providing an enclosure; and disposing at least one air pocket in theenclosure, the air pocket positioned farthest away from a location whereliquid begins to freeze in the enclosure.
 89. The method of claim 88,wherein the air pocket having a volume proportion to an amount of fluidin the enclosure.
 90. The method of claim 88, wherein the air pocketaccommodates a predetermined level of fluid expansion.
 91. The method ofclaim 90, wherein the predetermined level of fluid expansion is between5 to 25 percent.
 92. A method of preventing cracking of a liquid system,the method comprising the steps of: providing a housing having at leastone inlet chamber and at least one outlet chamber; and disposing atleast one air pocket in the inlet and outlet chambers, the air pocketpositioned farthest away from a location where liquid begins to freezein the chambers.
 93. The method of claim 92, wherein the air pockethaving a volume proportion to an amount of fluid in the chambers. 94.The method of claim 92, wherein the air pocket accommodates apredetermined level of fluid expansion.
 95. The method of claim 94,wherein the predetermined level of fluid expansion is between 5 to 25percent.
 96. An apparatus for preventing cracking of a liquid system,comprising: an enclosure for holding liquid having a plurality of walls;and at least one flexible object coupled to form a portion of at leastone wall of the enclosure such that pressure exerted on the flexibleobject increases a volume of the enclosure.
 97. The apparatus of claim96, wherein the flexible object accommodates a predetermined level offluid expansion.
 98. The apparatus of claim 97, wherein thepredetermined level of fluid expansion is between 5 to 25 percent. 99.The apparatus of claim 96, wherein the flexible object being capable ofcontracting and expanding between a minimum volume condition and amaximum volume condition.
 100. The apparatus of claim 96, wherein theflexible object being secured within the enclosure.
 101. The apparatusof claim 96, wherein the flexible object is made of one of thefollowing: rubber, plastic or foam.
 102. The apparatus of claim 96,wherein the enclosure is a tubing.
 103. An apparatus for preventingcracking of a liquid system, comprising: a housing for holding liquidhaving at least one inlet chamber and at least one outlet chamberstructure; and at least one flexible object coupled to form a portion ofat least one of the inlet and outlet chambers such that pressure exertedon the flexible object increases a volume of the housing.
 104. Theapparatus of claim 103, wherein the flexible object accommodates apredetermined level of fluid expansion.
 105. The apparatus of claim 104,wherein the predetermined level of fluid expansion is between 5 to 25percent.
 106. The apparatus of claim 103, wherein the flexible objectbeing capable of contracting and expanding between a minimum volumecondition and a maximum volume condition.
 107. The apparatus of claim103, wherein the flexible object being secured within the inlet andoutlet chambers.
 108. The apparatus of claim 103, wherein the flexibleobject is made of one of the following: rubber, plastic or foam.
 109. Amethod of preventing cracking of a liquid system, the method comprisingthe steps of: providing an enclosure for holding liquid having aplurality of walls; and disposing at least one flexible object to form aportion of at least one wall of the enclosure such that pressure exertedon the flexible object increases a volume of the enclosure, the flexibleobject accommodating a predetermined level of fluid expansion.
 110. Themethod of claim 109, wherein the predetermined level of fluid expansionis between 5 to 25 percent.
 111. The method of claim 109, wherein theflexible object being capable of contracting and expanding between aminimum volume condition and a maximum volume condition.
 112. The methodof claim 109, wherein the flexible object is made of one of thefollowing: rubber, plastic or foam.
 113. The method of claim 109,wherein the enclosure is a tubing.
 114. A method of preventing crackingof a liquid system, the method comprising the steps of: providing ahousing for holding liquid having at least one inlet chamber and atleast one outlet chamber; and disposing at least one flexible object toform a portion of at least one of the inlet and outlet chambers suchthat pressure exerted on the flexible object increases a volume of thehousing, the flexible objects accommodating a predetermined level offluid expansion.
 115. The method of claim 114, wherein the predeterminedlevel of fluid expansion is between 5 to 25 percent.
 116. The method ofclaim 114, wherein the flexible object being capable of contracting andexpanding between a minimum volume condition and a maximum volumecondition.
 117. The method of claim 114, wherein the flexible object ismade of one of the following: rubber, plastic or foam.
 118. An apparatusfor preventing cracking in a pump, comprising: a housing having at leastone inlet chamber and at least one outlet chamber; and a plurality ofspaced apart flexible objects coupled to form a portion of at least onewall of the housing such that pressure exerted on the plurality ofspaced apart flexible objects increases a volume of the housing. 119.The apparatus of claim 118, wherein the flexible objects accommodate apredetermined level of fluid expansion.
 120. The apparatus of claim 119,wherein the predetermined level of fluid expansion is between 5 to 25percent.
 121. The apparatus of claim 118, wherein the flexible objectsbeing capable of contracting and expanding between a minimum volumecondition and a maximum volume condition.
 122. The apparatus of claim118, wherein the pump is electro-osmotic.
 123. The apparatus of claim118, wherein the flexible objects are made of elastomer hinges.
 124. Theapparatus of claim 118, wherein the flexible objects are made of one ofthe following: plastic, rubber, or foam.
 125. The apparatus of claim118, wherein the flexible objects are fastened to rigid plates of thehousing.
 126. A method of preventing cracking in a pump, the methodcomprising the steps of: providing a housing having at least one inletchamber and at least one outlet chamber; and disposing a plurality ofspaced apart flexible objects to form at least one wall of the housingsuch that pressure exerted on the plurality of spaced apart flexibleobjects increase a volume of the housing, the plurality of spaced apartflexible objects accommodating a predetermined level of fluid expansion.127. The method of claim 126, wherein the predetermined level of fluidexpansion is between 5 to 25 percent.
 128. The method of claim 126,wherein the flexible objects being capable of contracting and expandingbetween a minimum volume condition and a maximum volume condition. 129.The method of claim 126, wherein the pump is electro-osmotic.
 130. Themethod of claim 126, wherein the flexible objects are made of elastomerhinges.
 131. The method of claim 126, wherein the flexible objects aremade of one of the following: plastic, rubber or foam.
 132. The methodof claim 126, wherein the flexible objects are fastened to rigid platesof the housing.